1. Field of the Invention
The present invention relates to a method for preparing a coloring layer composition for a chromatic device. A composition obtained by the method can be used in a coloring layer forming process for forming, for example, a reduction coloring layer of an electrochromatic (EC) device.
A known chromatic device, an EC device , for example, comprising a first transparent electrode layer 2, a reduction coloring layer 3, an electrolyte layer 4, an oxidation coloring layer 5, a second transparent electrode layer 6 and a second transparent substrate 7 successively laminated on a first transparent substrate 1 in show in FIG. 1. By applying a current of a predetermined threshold value or more between the first electrode layer 2 and the second electrode layer 6 in the EC device, a redox reaction takes place in the vicinities of the interfaces between the first and second electrode layers 2, 6 and the oxidation coloring layer 5 so as to obtain a reversible coloration-bleaching change.
The present inventors have proposed a coloring layer composition allowing reliable low cost production of such a large size chromatic device (U.S. Pat. No. 5,851,439). The composition is a peroxotungstic acid comprising a solute including WO.sub.3 .circle-solid.aNb.sub.2 O.sub.5 .circle-solid.bH.sub.2 O.sub.2 .circle-solid.cH.sub.2 O (a, b, and c represent 0 or a positive number), water for dispersing and holding the solute, and an organic solvent compatible with water.
Although bubbles are liable to be generated in the composition due to hydrogen peroxide contained in the peroxotungstic acid, the organic solvent compatible with water can control the generation of oxygen, caused by the decomposition reaction of the hydrogen peroxide, and the discharge of dissolved oxygen. Therefore, unevenness or peel-off of the coloring layer can be effectively prevented. Further, the organic solvent can be evaporated by heat treatment of the coat film without hindering the dissolution of the solute in the water. Accordingly, when the composition is employed, the practicality of a wet method, such as a dip coating method, is increased and a large size chromatic device can be reliably produced at a low cost.
However, according to the test results of the present inventors, it was learned that if a reduction coloring layer of an EC device is formed immediately after the preparation of the peroxotungstic acid, a sufficient coloring effect cannot be obtained with the EC device and further, the response speed of the coloration-bleaching change becomes slow.
Such a problem is observed not only in the EC device but also in other chromatic elements including a thermochromatic device, a photochromatic device, and the like.
In light of with the above-mentioned conventional situation, an object of the present invention is to provide a method for preparing a composition capable of reliably producing a large size chromatic device securely at a low cost, wherein the chromatic device has a sufficient coloring effect and a quick response speed of the coloration-bleaching change.